The present invention relates to a semiconductor integrated circuit device and a technology for manufacturing the same, and particularly to a technology effective for application to a semiconductor integrated circuit device having a SRAM (Static Random Access Memory).
A SRAM has been used as a cache memory used for a personal computer and a work station.
The SRAM comprises a flip-flop circuit for storing one-bit information therein and two information transfer MISFETs (Metal Insulator Semiconductor Field Effect Transistors). The flip-flop circuit comprises, for example, a pair of driver MISFETs and a pair of load MISFETs.
A problem associated with a soft error produced due to an α ray arises in each memory cell of such a memory. The soft error produced due to the α ray is a phenomenon in which an α ray contained in external cosmic radiation, or an α ray emitted from a radioactive atom contained in a package material for an LSI enters a memory cell and damages or corrupts information stored in the memory cell.
In order to take measures against such an α ray, a method has been discussed which adds capacitance to an information storage unit (corresponding to an input/output part of the flip-flop circuit) in the memory cell to thereby increase the capacitance of the information storage unit.
A technology for forming a capacitor or capacitance by polycrystalline silicon 10 connected to drain regions of FETs Qp′ and Qnd′, and polycrystalline silicon 11 connected to drain regions of FETs Qp and Qnd to thereby improve resistance to a soft error has been described in Unexamined Patent Publication No. Hei 11(1999)-17027, for example.
Further, there is disclosed in Unexamined Patent Publication No. Hei 10(1998)-163440 a technology for constituting a capacitor C by local wirings L1 and L2 at which input/output terminals of a flip-flop circuit for storing information therein are cross-connected, and a thin insulating film interposed between the two thereby to increase the capacity of a storage node of each memory cell, thus preventing a reduction in resistance to an α ray-based soft error.